Thermal circuit breaker



sept. 13, 1960 Filed April '7, 1959 J. ELLENBERGER 2,952,758

THERMAL CIRCUIT BREAKER 2 Sheets-Sheet 1 /N VEN TORI .Zn/L EL Lens se sm PITUVT SENT SCP- 13, 1960 .1. ELLENBERGER THERMAL CIRCUIT BREAKER 2 Sheets-Sheet 2 Filed April 7, 1959 /NVENTO,Q.' Jako a ELLE Namen farm/r ,45u/T United States Patent O THERMAL CIRCUIT BREAKER Jakob Ellenberger Altdorf near Numberg, Germany, as-

signor to Ellenlierger & Poensgen G.m.b.H., Altdorf, near Numberg, Germany, a firm of Germany Filed Apr. 7, 1959, Ser. No. 804,640

lClaims priority, application Germany Apr. 23, 1958 11 Claims. (Cl. 200122) The present invention relates to a novel design of a thermal circuit breaker of the type comprising a contact spring with a contact on its free end and a bimetallic spring which is adapted to pivot the contact spring into the connecting or disconnecting position by means of a rocking member which is pro-vided with a pair of opposite V-shaped recesses. In such circmtbreakers which are designed as quick-action or snap switches, the contacts are opened and closed rapidly in order to prevent them rom sparking. In some of the known switches of this type, the contact spring had three tongues. The central tongue of this spring consisted of two parts, the inner ends of which engaged in V-shaped recesses in a rocking member, while each of the two outer tongues was bent to have an S-shape whereby a snap action was produced. On its free end, the three-tongued spring had a contact which, in the connecting position, was in engagement with the contact of a birnetallic. spring. At the occurrence of an excess current, the bimetallic spring was heated and bent by the action of a heating coil so that the contact of the three-tongued spring was disengaged. At such an opening movement of the spring, the longer part of the central tongue was taken along so that it formed an acute angle relative to the shorter part of the central tongue. Due to the special design of the outer tongues, the longer part of the central tongue exerted a pressure upon the rocking member so that the latter would pivot about the inner edge of the shorter part of the central tongue whereby the snap action of the three-tongued spring would be released and the contacts be separated. This known switch had the disadvantage that the three-tongued spring had a very complicated structure which rendered the production of the switch rather dii-heult and made the switch rather expensive.

There has also been a prior disclosure of an overload switch which had a bimetallic spring and a contact spring. The bimetallic spring had a recess into which the contact spring was adapted to engage. Between the free movable end of the contact spring and the end of the recess in the bimetallic spring a coil spring was interposed, one end of which engaged with the bimetallic spring while the other end engaged with the contact spring. As soon as the bimetallic spring was heated and thereby bent, the coil spring would, after exceeding the dead-center position, suddenly become effective and bend the contact spring abruptly so that the contact thereon was disengaged from the opposite Contact and the entire circuit was interrupted. In order to attain a proper snap action, the coil spring had to be made quite strong with the result that relatively great forces were exerted upon the contact spring which caused a correspondingly severe bending of this spring. A switch of this type consequently had the disadvantage that fatigue failures of the contact spring `due to the strong alternating stresses thereon were liable to occur, resulting in a breakdown of the switch.

It is an object of the present invention to provide a '2,952,758 Patented Sept. 13, 1960 thermal circuit breaker of the above-mentioned type operating in the nature of a snap-action switch, which may be very easily manufactured and assembled, and in which the lmovable parts, that is, the contact spring and the bimetallic spring carry out only relatively small movements so that they will not suffer from fatigue failures and the life of the switch will be lengthened, and in which the contacts will be separated suddenly and properly and may be closed with a delay of such movement. A suitable delay of the closing movement is according to the invention to be attained especially if the contacts have automatically opened due to an excess current or heating from the outside and should again close automatically after a certain length of time. A further object of the invention is to provide a thermal circuit breaker of a design which may also be applied to a three-phase alternating current and which is designed to separate all three phases if an excess current occurs in any one of these phases.

For attaining these objects, the invention provides that the rocking member with the V-shaped recesses therein is mounted on the opposite ends of the contact spring and the birnetallic spring and that the contact spring engages in the respective V.shaped recess in the rocking member under an initial tension. Since the rocking member lies between the ends of the two mentioned springs, the end of the bimetallic spring forms the pivot point of the rocking member. When the bimetallic spring is heated and thus bends in one direction and when it cools off and thus bends in the other direction, the pivot point of the rocking member will automatically be shifted, whereby a tipping of the rocking member into one or the other position will occur suddenly when the movement or" the bimetallic spring has shifted the pivot point of the rocking member at the point of engagement of the end of the bimetallic spring with the apex of the V-shaped recess in the rocking member to a point slightly beyond a straight-line connection between the ends of the two springs and the central line connecting the apexes of the two V-shaped recesses in the rocking member.

Since the rocking member can pivot freely and since there is no fixed pivot point, a certain delay in the pivoting movement may be provided by preventing the movement of the rocking member to its tipping point from automatically resulting in an immediate tipping thereof to the other end position. This may be attained since it is possible to maintain a straight-line connection between the two springs during a certain pivoting range. The actual tipping of the rocking member, however, will result in a pivoting of the contact spring in one or the other direction, that is, from the closed position to the Open position of the contacts or vice versa. It is then immaterial whether the bimetallic spring will be bent by being heated Iindirectly by its heating coil which is energized by an excess current or whether the circuit breaker is acted upon directly by a heat source, for example, the windings of a motor.

The rocking member according to the invention is preferably made of a suitable insulating material in order to insulate the contact spring from the bimetallic spring. However, at least the V-shaped recess into which the bimetallic spring engages is preferably provided with a metallic lining in order to prevent undue wear on the rocking member itself. This metallic lining is also of importance insofar as it will protect the insulating ma` the bimetallic spring has to produce in order to operate the circuit breaker, the rocking member ma accordingv to another feature of the invention, be connected to or provided with a brake element which is adapted to engage with a cooperating brake surface at least during the pivoting movement of the rocking member in one direction. The brake element may for this purpose be provided with a Ibrake arm which is pivotable against the action of a spring only in one direction of the rocking movement of the rocking member. Consequently, the brake arm will yield resiliently only during the movement in one direction, for example, during the disconn necting movement, but not during the movement for closing the contacts in which an additional friction is thus produced. This friction requires that the bimetallic spring has to cool off considerably and produce a greater force in the direction toward the cold side until the tipping point is reached. The friction factor is then determined by the length of the friction surface, which will thus also determine the length of time of the return movement of the switch. Thus, if the length of the friction surface is increased, it will take a correspondingly greater length of time until the movement of the bimetallic spring will bring the rocking member to the tipping point.

The mentioned brake surface which is to be engaged by the brake arm on the rocking member is provided within the housing of the circuit breaker and preferably on a part of the housing, although it may, of course, also be provided on the cover of the housing. For increasing or reducing the length of the brake surface, the invention further provides the same or the part of the housing carrying the same to be adjustable relative to the brake arm on the rocking member.

In some instances it is desirable in a circuit breaker of this type that the contacts thereof will be retained in the open position even though the bimetallic spring has cooled off and would normally cause the contacts again to be closed. For this purpose, when the contact on the contact spring is in the open position, an arresting device which is provided with a release key is adapted to engage with the contact spring to retain it in the open position. When the release key is then depressed, the contact spring will again be released from the arresting device and move automatically to the closing position because of the pivotal movement of the rocking member.

The circuit breaker according to the invention may also be used as a three-pole relay for three-phase induction motors and similar apparatus by mounting three of these circuit breakers in a row behind each other within a common housing and by connecting them by means of a common rocking member. Such a circuit breaker requires only a single locking device which is adapted to engage with one of the three contact springs to arrest all of these springs in the open position, and which is releasable by a single release key. lf the circuit breaker is intended to operate only thermally, it is advisable to mount the same in a manner so as to permit the heat,

for example, of a motor winding, to act directly upon the bimetallic strip of the circuit breaker. For this purpose, the housing of the circuit breaker is preferably provided at one side with a perforated cover plate through which the outside heat may enter into the housing.

Further objects, features, and advantages of the present invention will become apparent from the detailed description thereof, particularly when read with reference to the accompanying drawings, in which- Figure 1 shows a side view of the thermal quick-acting circuit breaker according to the invention with its contacts being in the closed position;

Figure 2 shows a cross section taken along line II-II of Figure 1;

Figure 3 shows a perspective view of the rocker member according to the invention with the brake element thereon;

Figure 4 shows a View of the circuit breaker according to Figure 1, With its contacts in the open position;

Figure 5 shows a perspective view of the lower side of the housing of the circuit breaker;

Figure 6 shows a perspective view of the upper side of the housing; while Figure 7 shows a diagrammatic perspective view of a circuit breaker mechanism according to the invention used as a three-pole relay.

Referring to the drawings, and first particularly to Figures 1 to 6, the circuit breaker according to the invention is mounted within a housing 1 which is provided with a cover plate 2 with a plurality of apertures 3 therein for conducting the heat developed within the housing to the outside without, however, permitting any heat to pass from the outside into the housing, which is of importance if the circuit breaker is supposed to work purely thermally. A contact spring 5, the free end 6 of which carries a contact 7, is mounted in housing 1 at 4. Contact 7 cooperates with a contact 8 on a second contact spring 9 which is mounted in the housing at 10 and adapted to be adjusted to have a certain initial tension by means of a screw 11. Housing 1 -further contains a bimetallic spring 13 which is mounted at 12 and surrounded by a heating coil 14. This heating coil 14, as well as the contact spring 5, is conductively connected at @l to a terminal screw 15 to which a separate circuit may be connected. The free end 16 of the bimetallic spring 13 carries a screw 17 through which the heating coil 14 is conductively connected to the bimetallic spring which, in turn, is connected at its mounting point 12 to a terminal screw 1S. As shown particularly in Figure 6, a third terminal screw 19 isV mounted on housing 1 adjacent to screw 1S. This terminal screw 19 is connected to the second contact spring 9 and secures the same at 11i to the housing ll.

A rocking member 20 which preferably consists of a plastic material and has a substantially double-trapezoidal cross section, as shown particularly in Figure 3, is interposed between the free ends 6 and 16 of contact spring 5 and bimetallic spring 13 and provided with V- shaped recesses 21 and 22 in its opposite end surfaces which are associated with springs 5 and 13. Recess 22 is reinforced by a lining of sheet metal 23 in order to protect the rocking AInember 20 of plastic from being unduly worn when it is heated by the bimetallic spring 13.

Housing 1 further carries at 25 an arresting spring 24 which is disposed above the contact spring S and the hooked end portion 26 of which is adapted to pass through an aperture 27 in spring 5 and to engage with the lower side of this spring when the latter is bent to the position as shown in Figure 4. For releasing the contact spring 5 and disengaging it from the hooked end portion 26 of the arresting spring 24, a release key 28 is slidably mounted in housing 1 and adapted to be depressed against the action of a spring 29. As shown particularly in Figure 3, the rocking member 20` forms at one side a brake part 30 comprising a brake arm 31 which is adapted to be pivoted upwardly against the action of a spring 32 and to engage with a brake surface 33 on housing 1, as illustrated in Figures 1 and 4. The length of this brake surface 33 may be enlarged or reduced by providing it on a slide member 34 which may be adjusted toward the right or left, as viewed in Figure 1, by means of a screw spindle 35 which is mounted in housing 1 at 36. In order to prevent the slide member 34 from turning with spindle 35, it is provided with an angular projection which engages into a corresponding recess 37 in housing 1, as shown particularly in Figures 4 and 7. The cover plate 2 is preferably secured to housing 1 by hollow rivets 38 through which suitable screws may be inserted to mount the switch on a wall surface or on the apparatus which it is designed to protect or control.

The operation of the switch according to Figures 1 to 6 is as follows:

Normally, contacts 7 and 8 are in the closed position,

as shown in Figure l, in which the ends 6 and 16 of contact spring 5 and bimetallic spring 13 facing toward each other are offset relative to each other and the rocking member 20 lis disposed in an oblique position with respect to the direction of springs 5 and 13. If an excess current then occurs and heats the heating coil 14 which, in turn, heats up the bimetallic spring 13, or if the bimetallic spring is heated directly by the current owing therethrough, or if the bimetallic spring is heated by the temperature coming in from the outside, it will be bent downwardly. This, in turn, causes the pivot point of rocking member 20 at the free end 16 of -bimetallic spring 13 within recess 22 to shift slowly until the ends 6 and 16 of the springs assume a straightline direction with the center line connecting the apexes of the V-shaped recesses of rocking member 20. When the bimetallic spring then bends further downwardly, the rocking member will suddenly swing in a clockwise direction to the position as shown in Figure 4 and thereby abruptly separate contacts 7 and 8. If an arresting device such as the arresting spring 24 is provided, its free end 26 will during this upward movement of contact spring 5 pass through the aperture 27 in spring 5 and then engage with and arrest this spring in its bent position according to Figure 4.

During the sudden rocking movement of rocking member 20 as above described, the brake arm 31 has also passed over the brake surface 33. Since spring 32 then allowed brake arm 31 to yield resiliently, the rocking movement of member 20 could proceed practically without friction. If there is no arresting device 24 provided, bimetallic spring 13 will cool oif after contacts 7 and 8 are separated according to Figure 4 and slowly swing back to its upper starting position. During this upward movement of the bimetallic spring 13, rocking member 20 will also be shifted upwardly since it is freely suspended between the ends of springs 6 and 16. Such dislocation of rocking member 20 will result in a delay of the tipping movement thereof. A further delay results from the fact that the brake member 31 will during this movement slide nonresiliently along the brake surface 33. The length of such delay also depends upon the adjustment of this brake surface by screw 35. Only after the brake member 31 has slipped of the brake surface 33 and. when rocking member 20 has reached the tipping point, that is, when the ends of springs 6 and 16 are in a straight line with the center line of rocking member 20, the latter will be able to swing back to the position as shown in Figure l, in which contacts 7 and 8 will automatically engage.

Although if the arresting spring 24 is provided, the bimetallic spring 13 will likewise cool oi after contacts 7 and 8 are separated, such cooling will have no effect since contact spring 5 will be held arrested inthe bent position by spring 214. If the release key 28 is then depressed to disengage the arresting spring 24 from Contact spring 5, the latter will swing back to the contact-closing position, and such movement will proceed rapidly because of the cooperation of the spring tension of contact spring 5 4with the spring tension of bimetallic spring 13 through rocking member 20.

Figure 7 illustrates a modification of the circuit breaker according to the invention which is designed to form a three-pole relay, for example, for a three-phase induction motor. It will be seen that all of the elements contained in the circuit breaker according to Figures 1 to 6 are provided three times, except the housing 1 (not shown) with its cover 2 and the rocking member 20 with the brake part 30 and brake surface 33, and the arresting spring 24 with its release key 28. The individual contact springs 5 and 9 and the parts connected thereto, as well as the bimetallic springs 13 are disposed behind each other and connected by a single rocking member 20. Since there is only one arresting spring 24 provided, only one of the contact springs 5 has to have an aperture 27 for receiving the arresting spring. Since the switch according to Figure 7 in eifect forms three switches according to Figures 1 to 4 behind each other, rocking member 20 is also approximately three times as long as that shown in Figures l to 4.

As will be clearly apparent from Figure 7, the rocking member 20 may be lslipped from `one side or the other between the ends 6 and 16 of springs 5 and 13. This facilitates the installation of the switch considerably especially if suitable provision is made that the rocking member 20 may be inserted from the open side of the housing 1, as shown in Figure 5. ln that case, the brake part 30 would be shaped inversely to that shown in Figure 3 and mounted at the end of rocking member 20 `opposite to that on which it is mounted in Figure 3, so that it will face toward the cover plate 2 of the housing on which the brake surface 33 will then be provided either rigidly or adjustably.

The principal advantage `of the present invention consists in the fact that the rocking member 20 as distinguished from previous circuit breakers with snap contacts does not have a fixed point of location, so that very long lreturn periods yare attainable. The invention affords the additional advantage that the switch operation may be delayed due to the fact that the bimetallic spring has to accumulate a greater force until it can swing lto the position in which the tipping point of the rocking member will be reached, and that the sudden tipping of the rocking member produces a pivoting of the end 6 of contact spring 5 and Athus either a sudden separation or closing of contacts 7 and 8. As distinguished from the known circuit breaker designs of this type, in which the bimetallic yspring directly effects a relative movement of the contacts, the contact spring of the circuit breaker according to the invention is moved from one to the other position by the intermediate action of a rocking member which pivots about the free end '16 of the bimetal-lic spring 13.

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, I wish to have it understood that it is in no Way limited to the details of such embodiments, but is capable of numerous modications within the scope of the appended claims.

Having thus lfully disclosed my invention, what I claim 1s:

1. A thermal circuit breaker comprising a contact spring mounted at one end and bent at its opposite end into a U-shaped conguration, said contact spring carrying a contact on the free of the U, a second contact adapted to be engaged by said first contact, a normally lsubstantially straight bimetallic spring mounted at one end, Iand a rocking member having a pair of opposite V-shaped recesses therein interposed between and receiving, respectively, the free end of said free leg of said contact spring and the free end of said bimetallic spring, said rocking mem-ber being :adapted to be freely movable on said free ends Within said recesses, said contact spring engaging into one of said recesses under an initial tension, said bimetallic spring when heated being adapted to bend and through said rocking member to swing said contact spring and the contact thereon to a connecting and disconnecting position relative to said second contact.

2. A circuit breaker as deiined in claim l, wherein said rocking member consists of insulating material, :and further comprising a metal lining within at least one of said V-shaped recesses.

3. A circuit breaker as defined in claim l, further comprising a brake member connected to said rocking member, and a member having a brake surf-ace thereon, said brake member being adapted to engage said brake surface at least in one direction of the reciprocating movement of said rocking member.

4. A circuit breaker as defined in claim 3, wherein said brake member comprises a supporting member mounted on said rocking member, a Ibrake arm pivotally mounted on said supporting member, and a spring `acting upon said brake arm, said brake arm being adapted to be pivoted in one direction of the reciprocating movement of said rocking member against the action of said spring.

5. A circuit breaker as defined in claim 3, further comprising a housing containing said circuit breaker, said brake surface being disposed on :and within said housing.

6. A circuit breaker as defined in claim 3, further comprising means for adjusting the position oit said brake surface relative to said brake member.

7. A circuit breaker as defined in claim 5, further comprising means for adjusting the part of said housing containing said brake surface relative to said brake member.

8. A circuit breaker as defined in claim 1, further comprising means for arresting said contact spring in the open position of said contacts, and means for releasing said arresting device from said spring engaging position.

9. A 'circuit breaker comprising a housing, three contact springs, each mounted at one end Within said ho-using and in a spaced relation behind each other, each of said contact springs being bent at `its opposite end into a U-shaped configuration, said contact spring carrying a contact on the free leg of the U, second contacts mounted Within said housing, each adapted to cooperate with one of said first contacts, three normally substantially straight rbirnetal-lic springs, each mounted at one end within said housing, a common rocking member having a pair of opposite V-shaped recesses therein interposed between and receiving, respectively, the free ends of said lfree legs or said contact springs and the free ends of said -bimetallic springs, said rocking member being adapted to be lfreely movable on said free ends within said recesses, said contact .springs engaging under an initial tension into one of said recesses, each of said bimetallic springs when heated being adapted to bend and through said conm-on rocking member to swing said Contact lsprings. and the contacts thereon to a connecting and disconnecting position relative to said second contacts.

10. A circuit breaker `as defined in claim 9, further comprising a single arresting means mounted Within said housing and adapted to engage lwith one of Vsaid contact springs, land a release key mounted in a wall of said housing and being adapted to be depressed from the outside of said housing for disengaging said varresting means `from said contact spring.

1l. A circuit breaker as defined in claim 1, further comprising a housing containing said circuit breaker and having at least one open side, and a perforated plate secured to said yhousing for closing said side while permitting dissipation of heat produced within said housing.

References Cited in the file of this patent UNITED STATES PATENTS 2,068,374 Carlson Ian. 9, 1937 2,313,341 Holmes Mar. 9, 1943 2,695,524 Eaton Nov. 30,1954 2,872,548 Christensen Feb, 3, 1959 

